BCM43455 Preliminary Data Sheet
Frequency Selection
Frequency Selection
Any frequency within the ranges specified for the crystal and TCXO reference may be used. These include not
only the standard handset reference frequencies of 19.2, 19.8, 24, 26, 33.6, 37.4, 38.4, and 52 MHz, but also
other frequencies in this range, with approximately 80 Hz resolution. The BCM43455 must have the reference
frequency set correctly in order for any of the UART or PCM interfaces to function correctly, since all bit timing
is derived from the reference frequency.
Note: The fractional-N synthesizer can support many reference frequencies. However, frequencies
other than the default require support to be added in the driver plus additional, extensive system
testing. Contact Broadcom for further details.
The reference frequency for the BCM43455 may be set in the following ways:
•
Set the xtalfreq=xxxxx parameter in the nvram.txt file (used to load the driver) to correctly match the crystal
frequency.
•
Auto-detect any of the standard handset reference frequencies using an external LPO clock.
For applications such as handsets and portable smart communication devices, where the reference frequency
is one of the standard frequencies commonly used, the BCM43455 automatically detects the reference
frequency and programs itself to the correct reference frequency. In order for auto frequency detection to work
correctly, the BCM43455 must have a valid and stable 32.768 kHz LPO clock that meets the requirements listed
in Table 3 on page 33 and is present during power-on reset.
Broadcom®
November 5, 2015 • 43455-DS109-R
Page 32
BROADCOM CONFIDENTIAL
CYPRESS [ CYPRESS ]
